The table and graph have the corrected flow data for the intake tract at 28 inches based on Kibblewhite's flow bench. The valves are 2mm oversize. Test 1 is the bare head with clay shaped in a radius around the entry. Test 2 is the head with carb and a long K and N filter with sock bolted directly onto the carb end. Test 3 is the head, carb, a bellmouth, a plenum 1.2 times the cylinder volume, and a shorter K and N air filter with a sock. Test 4 is the same as Test 3 except the walrus valve, a sort of anti-reversion valve, is between the filter and the plenum.
The two intake arrangements in Test 2 and 3 will be tested on the dyno. The walrus valve goes into the recycle metal bin.
As per the equations in Harold Bettes' Engine Airflow book on pp 82 and 83, with an 8 percent HP loss between the engine and rear wheel added to the formula, the engine is estimated to make 114 HP at the rear wheel at 9,350 rpm. This is a very reasonable estimate based on past experience.